Page 29 - PC 101 practical notes 24-25..

MANSOURA NATIONAL UNIVERSIY
PHARM D- CLINICAL PHARMACY LEVEL I PHARM. ANAL. CHEM. I (PC 101)

but without the sample and the E.P. in this case is called

Blank Reading.

 Blank determination is required in this experiment because

when NaOH is heated and then cooled, its strength is decreased due to:

1- Interaction of NaOH with the glass of the flask.

2- Absorption of atm. CO 2.

More explanation about blank determination:

Sample + 50 ml 1 N NaOH  ⎯
⎯⎯ 50 ml of 1 N NaOH ⎯→
  x ml 

Main experiment titrate the remaining with the unreacted part CO 2 loss due to reactn. with glass &

Boil


remaining
part
Cool
reacted

(x ml)

sample
unreacted part of 1 N NaOH
≠ 1 N HCl

[E.P. = x ml]
 Titr. ≠ 1 N HCl
E.P.

50 ml 1 N NaOH  ⎯
⎯⎯ 50 ml of 1 N NaOH ⎯→

Blank determination unreacted part of 1 N NaOH the volume consumed from CO 2 
Boil


remaining unreacted part
Cool


Titr. ≠ 1 N HCl
titrate the remaining


≠ 1 N HCl
[Blank reading]

ex: 49.8, 49.9...etc
loss due to reactn. with glass &
Blank reading titrant (1 N HCl) is called

 The part reacted with the sample = (Blank reading – E.P.)

29 | P a g e